If you as an operative decide to take on the responsibility of commisioning an appliance that you have not installed yourself you will take full responsibility for the installation !
If the installation is subsequently inspected the install becomes yours & you will be held responsible for any defects that were found & you would be expected to put them right ! This would also include relevant electrics , condensate disposal , compliance with building regs & energy effiency !
Further to this if the property was subsequently sold the new owners would also consider the person who's name appears on any documentation as the profesional & responsible person should any issues arise !
I'd only commision and register a system/boiler that was installed to current standards anyway. I supose the gamble for the OP would be having to redo incorrect work e.g. PRV/condense/electrics or using TRV's only and no room stat.